1. Field of the Invention
The present invention relates to a brake control device which is provided with an abnormality detection function which enables a brake abnormality to be detected even during robot operation.
2. Description of the Related Art
The servo motors which control the axes of a robot are equipped with electromagnetic brakes. The electromagnetic brakes hold the posture of the robot during an emergency stop of the servo motors, so are used for shortening the stopping distance when the servo motors make an emergency stop.
In recent years, to reduce the energy consumption of the robot, the robot controller has to deliberately engage the electromagnetic brakes so as to eliminate the power for maintaining the posture of the robot even when a robot temporarily stops during operation.
When electromagnetic brakes are engaged/disengaged while the robot temporarily stops during operation in this way, the number of times the electromagnetic brakes are engaged/disengaged greatly increases. If forming the brake drive control circuit by relays or other contact circuits, the brake drive control circuit will immediately end up reaching the end of its service life. For this reason, to realize high frequency operation such as engagement/disengagement of the electromagnetic brakes even when a robot is temporarily stopped, the brake drive control circuit has to be formed by semiconductor circuit.
However, a semiconductor circuit is liable to malfunction due to temporary overvoltage or short-circuiting etc. or is liable to malfunction due to short-circuiting of output due to incidental defects in parts. Further, if the output short-circuits, the brake ends up being disengaged (brake is rendered nonoperating) while the robot is in emergency stop condition. It becomes impossible to hold the posture of the robot and becomes extremely dangerous. For this reason, it is absolutely necessary to detect single fault of the brake circuit and to have the brake operate normally even at the time of malfunction.
In view of this, Japanese Patent Publication No. 2006-123118A discloses a brake drive control circuit 10 such as shown in FIG. 1A which can detect a semiconductor malfunction of a brake circuit. The brake drive control circuit 10 which is disclosed in Japanese Patent Publication No. 2006-123118A is formed by provision of two semiconductor switching devices Tr1 and Tr2, a brake B to which a surge absorber SA is connected in parallel, and a detection circuit D. The two semiconductor switching devices Tr1 and Tr2 are connected in series through the detection circuit D between the power supply and the ground (0V). The contact points C1 and C2 between the two semiconductor switching devices Tr1 and Tr2 of the detection circuit D are connected to the two ends of the brake B. The two semiconductor switching devices Tr1 and Tr2 turn on when the brake signals BS1 and BS2 are input. Further, the detection circuit D is for example comprised of a photo coupler and outputs a detection signal DS when voltage is applied to the brake B.
FIG. 1B shows the operation of the detection circuit D when the two semiconductor switching devices Tr1 and Tr2 are normal. In the test period, a high level brake signal BS1 or BS2 is input to just one of the two semiconductor switching devices Tr1 and Tr2. At this time, the other semiconductor switching device is turned off, so current does not flow to the detection circuit D and the detection circuit D does not output a detection signal DS. Further, when disengaging the brake (described in figure as “BRAKE DISENGAGED”), high level brake signals BS1 and BS2 are input simultaneously to the two semiconductor switching devices Tr1 and Tr2. At this time, the two semiconductor switching devices Tr1 and Tr2 are both turned on, so current flows to the detection circuit D and a high level detection signal DS is output from the detection circuit D.
FIG. 1C shows the operation of the detection circuit D at the time of an abnormality at one of the two semiconductor switching devices Tr1 and Tr2 such as short-circuiting of the switching device Tr1. When, in the test period, a brake signal BS1 is input to only the semiconductor switching device Tr1, the semiconductor switching device Tr2 is normally off, so current does not flow to the detection circuit D. The detection signal DS is not output from the detection circuit D. On the other hand, when the brake signal BS2 is input only to the semiconductor switching device Tr2, if the semiconductor switching device Tr1 is normal, it is off, so current does not flow to the detection circuit D, but if the semiconductor switching device Tr1 is abnormal, current ends up flowing to the detection circuit D.
Due to this configuration, when one of the two semiconductor switching devices Tr1 and Tr2 is malfunctioning and short-circuits, during the test period, current flows to the detection circuit D, so an alarm can be issued to report abnormalities of the semiconductor switching devices Tr1 and Tr2 and cut power to the brake drive control circuit 10. If cutting power to the brake drive control circuit 10, current no longer flows to the brake B and the brake B operates. In this way, in the art of Japanese Patent Publication No. 2006-123118A, it is possible to prevent the brake from becoming unable to be locked due to a single fault of the switching control means and possible to improve the safety when controlling drive of a brake.
However, the brake circuit is tested for malfunction by the brake drive control circuit 10 which is disclosed in Japanese Patent Publication No. 2006-123118A only one time during the test period right before the brake is disengaged as shown in FIG. 1B. The brake circuit cannot be tested during the subsequent operation. For this reason, to again test the brake circuit, it is necessary to stop the operation of the robot and turn off the power from the brake drive control circuit 10. If not testing the brake for a long period of time, there is a possibility that a single fault will become a double fault and there is the danger that the brake will no longer operate normally. When a high reliability of the brake drive control circuit 10 is demanded or when continuous operation of the robot over a long period is necessary, it is necessary to test the brake drive control circuit 10 during robot operation, but there was the problem that this was not possible with the brake drive control circuit 10 which is disclosed in Japanese Patent Publication No. 2006-123118A.